NEW YORK (Reuters Health) - Babies treated with antibiotics for middle-ear and other infections may have increased odds of developing inflammatory bowel disease later in childhood, a small study suggests.

Canadian researchers found that among 36 children with either ulcerative colitis or Crohn's disease -- the two main forms of inflammatory bowel disease (IBD) -- 58 percent had been prescribed at least one course of antibiotics in the first year of life.

In contrast, only 39 percent of 360 IBD-free children studied for comparison had taken antibiotics during their first year.

The findings, published in the American Journal of Gastroenterology, do not prove that early antibiotic use causes IBD in some children. But they support the theory that factors affecting the early-life balance of "good" and "bad" bacteria in the intestines may contribute to IBD.

Both colitis and Crohn's disease are marked by chronic inflammation in the intestines, leading to symptoms like abdominal pain and diarrhea. The conditions are thought to arise from an immune-system overreaction that injures the body's own intestinal tissue, but the underlying reasons for the aberrant immune response are unclear.

There is a genetic component to IBD, since the conditions can run in families. However, experts believe that environmental triggers -- such as diet, an infection, or exposure to tobacco smoke - likely combine with genetic susceptibility to cause IBD in some people.

The new study appears to be the first to draw a connection between confirmed early antibiotic use and childhood IBD, according to the researchers.

The design of the study does not, however, allow any conclusions about cause-and-effect, senior researcher Dr. Charles N. Bernstein, of the University of Manitoba in Winnipeg, told Reuters Health in an e-mail.

Larger studies, as well as lab research into the effects of common antibiotics on different types of intestinal bacteria, are still needed, he said.

In theory, early antibiotic use could create an imbalance in the potentially beneficial and potentially harmful bacteria that establish residence in the gut during the first year of life. If the composition of these intestinal "microflora" is altered, the immune system may begin to react abnormally to some of the bacteria.

For the current study, Bernstein and his colleagues analyzed medical records for 36 children diagnosed with either ulcerative colitis or Crohn's between 1996 and 2008, at an average age of 8. Each child was compared with 10 IBD-free children of the same age, sex and area of residence.

The researchers found that children with IBD were more likely to have been prescribed an antibiotic during the first year of life -- most commonly for middle-ear infections, but also for respiratory and other types of infection.

Overall, antibiotic use in infancy was linked to a tripling of the risk of IBD relative to children who had no antibiotic prescriptions in their first year of life.

While that relative increase in risk is large, any one child's absolute risk of developing IBD from antibiotic use -- if the medications are, in fact, to blame -- would be small, according to Bernstein.

In the U.S., it's estimated that just over 1 million people have IBD, with new cases diagnosed at a rate of 10 per 100,000 people each year.

It is still possible that factors other than the antibiotics themselves explain the link between early use of the medications and IBD risk. One alternative, according to Bernstein, is that certain conditions for which antibiotics are used -- like middle-ear infections -- are related to IBD risk.

However, he added, the biological mechanisms that would underlie such a connection are not clear.

For now, Bernstein said, the findings offer a reminder "to avoid indiscriminate use of antibiotics when we can." Parents should be aware that antibiotics are often unnecessary for respiratory infections; in fact, many are caused by viruses and do not even respond to antibiotics, which target bacteria, he said.

As for the middle-ear infections so common in infancy, about 80 percent of children get better without antibiotics, according to the American Academy of Pediatrics. In its treatment guidelines, the academy says that infants and children without severe symptoms can often wait 48 to 72 hours before starting antibiotics to see if the infection improves on its own.

SOURCE: link.reuters.com/fec92q American Journal of Gastroenterology, online October 12, 2010.

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